According to Odian, Principles of Polymerization, 2nd Ed., Wiley-Interscience, p. 18, (1981) polymers fall into three structural groups: linear, branched and crosslinked. Branched polymer molecules are those in which there are side branches of linked monomer protruding from various central branch points along the main polymer chain and that have several idealized configurations. Branched polymers are known in at least three configurations. They may be "comb-like" where each branch is of equal length, "dendritic" where branches occur on branches (series branching), or "star-like" where all branches radiate from a single point.
Branching often imparts various desirable properties, for example, branched polymers have been made that have improved melt flow and processability. Additionally, appropriate branching disrupts long linear polymer backbones to thereby reduce crystallinity. In free radical and cationic polymerization processes, for example in the production of polyethylene, branching is largely uncontrolled and its extent is dependent on polymerization variables. In some cases branching can be as high as 15-30 branches per 500 monomer units. In contrast, anionic polymerization processes yield very narrow molecular weight distributions and a unique structure. Branched polymer structures produced by anionic polymerization are generally star shaped (arrayed about a central point or nucleus) although the structure can be varied by coupling together individually prepared arms of different structure.
Such polymers are described by St. Clair in U.S. Pat. No. 4,391,949 where "asymmetric" star block copolymers are prepared by mutually linking together individually prepared living polymers, which may be represented by (AB)Li and (C)Li, with polyalkenylaromatic linking reagents. The structural formula describing the resulting polymer is given as (A-B).sub.x -Y-(C).sub.z. where x plus z is greater than six. A statistical distribution of polymer products would be obtained from this process, where the average structure is equal to the mole ratio of the respective charges. Further chain growth would only be possible through the linking nucleus Y.
Crossland, U.S. Pat. No. 4,010,226, has also recognized the problem of preparing block polymers with an asymmetric configuration and, to avoid the statistical distribution of polymers obtained by St. Clair, first coupled a set of polymer arms with divinylbenzene, then continued the polymerization, utilizing the anionic centers that remain on the divinylbenzene residue, to produce a different set of arms bound to the same nucleus. The number of new arms grown would thus equal the number of arms coupled together, since linking with divinylbenzene (DVB) is a non-terminating process and each newly grown arm would have an anionic terminus. Fahrbach, U.S. Pat. No. 4,086,298, discloses star-block copolymers having a mixture of arms where some arms are formed by first polymerizing styrene with alkyllithium to form living polymer blocks, represented by (A)Li, and then adding a mixture of styrene and butadiene to form a graded copolymer represented by A-B.fwdarw.A' where the arrow represents a graded segment. Other arms are made up of only the butadiene-styrene graded copolymer segment. These arms are then linked together with a polyfunctional coupling agent, such as DVB, to give star-branched polymers. U.S. Pat. Nos. 4,221,884, 4,248,980, 4,248,982, 4,248,983, and 4,248,984, Bi and Milkovich, describe a similar series of polymers in which more complex polymer arm segments are linked together using a polyalkenyl aromatic, such as divinylbenzene, to form an asymmetric star molecule.
Prudence (U.S. Pat. No. 3,949,020) prepares branched block polymers by a method wherein divinylbenzene is added with the diolefin monomer to a polystyryllithium initiator. However, according to Bi and Fetters (Macromolecules 9, 732-742 [1976]), such a method leads to gelation when the divinylbenzene/initiator ratio is three or greater.
Martin, in U.S. Pat. Nos. 4,080,400, 4,143,089, 4,148,838, and 4,273,896, describes a composition obtained from the linking together of anionically active polymers (from, e.g., styrene) with silanes of the formula, X.sub.4-a-b Si(R).sub.b (CH.dbd.CH.sub.2).sub.1, where X is a displaceable group, R is alkyl, a is 1 to 4 and b is 1 to 3. One of the stated objects of these patents is to couple polymeric carbanions with silanes and then form new carbanions which can be used to initiate the polymerization of cyclic silicones or "other unsaturated monomers". No disclosure is provided directed towards the step of using other unsaturated monomers except for certain unspecified hydrocarbon/siloxane block polymers.
It has been established [Nametkin, Chemical Abstract Nos. 85:47314a (1976), 87:185046g (1977), and 89:110569n (1978)] that vinylsilanes of the type described by Martin will copolymerize in an anionic fashion, for example with butadiene; however, reactivity is very low, with up to 300 hours required for good conversion. Furthermore, copolymers of vinyl silanes with dienes initiated by butyl lithium are unimodal but exhibit peak broadening due to the occurrence of chain termination reactions caused by spontaneous cleavage reactions producing lithium hydride (Nametkin, Chemical Abstract No. 93:168679x, 1980). Loss of LiH during anionic homopolymerization of vinyltrimethylsilane has also been observed and has been used to explain the poor conversion and spread in molecular weight distribution observed in these polymers [Nametkin, Dokl. Nauk SSSR, 215, 861 (1974)]. Chaumont [Eur. Poly. J. 15, 537 (1979)] prepared vinylsilyl terminated polystyrenes via anionic polymerization; however, it was necessary to cap the polymer anion with diphenylethylene in order to reduce side reactions.
Chlorosilane-substituted styrenes are well-known compounds and have been used, for example, to prepare polysiloxane macromolecular monomers [Kawakami, Polymer J., 14, 913 (1982)]. Chromatography gels have been described based on poly-.alpha.-methylstyrene dianions and chlorodimethylsilylstyrene [Greber, Angew. Makromol. Chem. 1971, 16/17, 325]. Compositions for the encapsulation of electrical equipment have been derived from organosilicon monomers having styrenyl groups (Lewis, U.S. Pat. No. 2,982,757). Hirao et al. (Macromolecules 1987, 20, 242) has studied the anionic homopolymerization of (4-alkoxysilyl) styrenes and reaction of the resultant homopolymer with polystyryllithium.
There has been no disclosure, however, of the use of organometallic-substituted styrenes, e.g., chlorosilanesubstituted styrenes, in the preparation of condensed phase polymers.